This invention relates to a sound absorbing heat shield having a perforate support layer on which a sound absorbing heat damming, or insulating, layer is attached, with the insulating layer having a protective coating on both sides thereof.
Such heat shields are used, among other places, in the automobile industry to case, or line, for example, interiors of tunnels or pipings of floor portions of motor vehicles. Such a casing is very important today because temperatures of exhausts, and thereby also temperatures of exhaust pipes, are substantially increased today with normal use of catalytic converters; and, on the other side, threshold values of motor-vehicle noise levels are continually set lower. For example, it is anticipated that standards in the European community for 1991 will be reduced to about half of normal noise levels today for commercial vehicles.
Previously-known heat shields have been predominantly of thick sheet metal parts with high heat reflection capabilities, preferably of aluminum, with heat absorbing insulation layers having protective foil thereon. The thusly used insulation layers are normally respectively of ceramic-, stone-, or glass-wool foams. These heat shields, however, are not particularly acoustically effective because sound waves will be, to a large extent, reflected. Such a heat shield is, for example, described in DE-U-8700919.6.
It has therefore also already been suggested that instead of using a relatively thick sheet metal part, one should use a metallic mesh or an expanded metal and to coat both sides of an insulation layer thereof with a protective foil. Such heat shields indeed display improved sound absorbing characteristics, however, they have not found particular success in the practice. For one thing, a metallic braid or mesh, or an expanded metal creates sawtooth like structures at deformed areas and in particular at flange, or peripheral edge, areas or zones which damage the thin protective foils. Also, attachment areas of these heat shields break away easily and must, therefore, be provided with additional mounting attachment elements. Such measures indeed prevent a ripping or breaking away from heat-shield mounting supports; however, because of this increased expenditure, they increase the difficulty and costs of mounting these heat shields. A further substantial disadvantage of such a heat shield is that an outer edge thereof cannot be completely sealed by means of a flange so that insulation material can absorb moisture thereat.
It is therefore an object of this invention to provide a sound absorbing heat shield which does not have these disadvantages of such known apparatus.
In particular, it is object of this invention to provide a stable shield which has distinct heat- and sound-absorbing characteristics which can be manufactured in an uncomplicated manner, allows a reliable mounting or attachment thereof, and which shows substantially no fatigue or sign of wear after relatively long use.